US1989671A - Spark plug - Google Patents

Description

Feb. 5, 1935. F. M. ANTHONY 1,989,671

SPARK PLUG Filed Nov.,28, 1931 FIG. I.

INVENTOR FELIX M. ANTHON ATTORNEY Patented F eb. 5, 1935 UNITED STATES PATENT OFFICE SPARK PLUG Felix M. Anthony, Piedmont, Calif., assignor o1 one-fourth to Kenneth G. Gillis and one-fourth 3 Claims.

. This invention relates to improvements in spark plugs and more particularly to the ground terminals of spark plugs for internal combustion engines.

The principal object of the invention is to arrange and design the ground terminal to compensate for its expansion and contraction to maintain an accurate spark gap between the electrode terminals at all engine temperatures.

Other objects and advantages appear as the description progresses.

Broadly stated, the invention consists of arranging the ground terminal to form a reverse curve. The two branches of the curve expand and contract in opposite directions; thus each compensates for the movements of the other, maintaining the end of the terminal in a fixed position with respect to the positive electrode of the spark plug.

In this specification and the accompanying drawing the invention is disclosed in its preferred form. It is to be understood, however, that it is not limited to this form because it may be embodied in other forms within the purview of the claims following the description.

In the one sheet of drawings:

Fig. 1 is a side elevation of a spark plug having electrode terminals constructed in accordance with this invention.

Fig. 2 is an end view of the same from below.

Fig. 3 is an enlarged vertical section of the lower portion of the spark plug diagrammatically showing the directions of the movements of the curved portions of the ground terminal during expansion.

In detail the construction illustrated in the drawing comprises the outer shell 1 having the threaded neck 2 for engaging the cylinder head of the motor, not shown. The shoulder 3 provides for compressing the usual gasket against the cylinder head when the shell is screwed into place by means of the hexagonal portion 4.

The center bore of the top portion of the shell is internally threaded to receive the bushing 5, having the hexagonal head 6.

The dielectric core 7 is usually formed of porcelain, compressed mica, or other refractory insulating material. This core extends through the shell 1 and is held in fixed position by screwing down the bushing 5 which forces the core against a suitable shoulder provided within the shell 1.

The center electrode 8 extends entirely through the core and is threaded at its upper end to engage the conventional terminal coupling 9. The

REESSUED lower end of the electrode projects through the core '7 and terminates in the fiat end 10 beyond the edge of the shell.

The structure thus far described is the construction of the conventional spark plug, the mechanical characteristics of which will vary With the type of motor in which it is used. It will be obvious to those skilled in the art that the present invention may be applied with suitable modifications to any of the existing types of 10 spark plugs.

The superiority of spark plugs in which the spark gap is located coincidentally with the axis of the spark plug has been long recognized by the art. However, it has been found to be impractical to use this type of spark plug due to variations in the length of the spark gap under varying temperatures. In prior constructions having this type of spark gap, the ground terminal is fixed in the outer shell and invariably has a single bend to bring the end of the terminal into proximity with the center electrode. As the spark plug becomes heated, the bent portion of the ground terminal tends to partially straighten out, thus greatly increasing the length of the spark gap. This prevents a sufiicient volume of current bridging the gap to form the hot spark necessary in modern internal combustion motors.

It is the purpose of the present invention to render practical the use of spark plugs having a spark gap located coincidental with the axis thereof. This is accomplished by designing the ground terminal to maintain an accurate spark gap at all temperatures of engine operation.

The ground terminal 11, provided by this invention, is fixed at 12 to the edge of the shell 1 and is bent at 13 toward the center electrode forming a semicircular arc. The terminal is bent in the opposite direction at 14 to form an are joining the arc 13 at 15 to form a reverse curve. The are 14 has a shorter radius than the arc 13, the ratio of the two radii being substantially two to one.

The end portion 16 of the terminal extends tangentially from the are 14 and lies in juxtaposition with the end of the center electrode leaving the spark gap 18 of the usual clearance. The terminal end 16 is preferably partially flattened to form a plane parallel with the fiat end 10 of the electrode to increase the sparking area. It is desirable that the flattening 16 should be so performed to leave the fillet 19 to reinforce the arc 14.

The lower portion of the bent terminal should be located below the terminal end 16 to drain away any accumulations of oil from the spark gap.

As the engine becomes heated, the 'arc 13 in the ground terminal expands and begins to straighten out in the direction of the arrow :1; (see Fig. 3). However, the are 14 expands and straightens out inthe oppositedirection as'indicated by the arrow 1: and compensates for the expansion of the are 13, thus maintaining the terminal end 16 in fixed position with respect to the end of the center electrode. 7 7

To secure perfeet compensating expansion action of the ground terminal it is important that the approximate proportions of the branches of the reverse curve be maintained in manufacture.

The longer radius and length of the are 13 is determined several factors in the operation of the spark plug. 1

It is to;be noted that the temperature of the ground terminal varies throughout its length. The heat of the portion forming the are 13 is largely conducted away through the adjacent shell 1 into the larger relatively cool body of the cylinder head. The are 14 being adjacent the intense heat of the spark reaches a greatlyl'higher temperature than the are 13. This requires the are 13 to be of larger radius and length to increase the distance of its expansion to compensate for the greater angular expansion of the more heated 81p 14. i

n The partial flattening pf the terminal end 16 also reduces the thickness of the terminal 11 at the are 14. As this flattening of the cross section at the are further increases its angular expansion, it provides further necessity for the larger size of the are 13.

Having thus described this invention, what I claim and desire to secure by Letters Patent is:

1. A spark plug having ashell; an insulated electrode in said shell; and a ground terminal having one end fixed in said shell and its free end in juxtaposition to said electrode to form a spark gap of predeterng ined width the ground terminal being bent into ajreverse curve with unequal radii, the greater radius being adjacent said shell, the cross section of said terminal being flattened transversely to the plane of the radius of the curve adjacent said electrode, all combined and arranged to maintain substantially the predetermined t idth of said spark gap under working temperature variations.

i 2. A spark plug having a shell, an insulated electrode in said shell, a ground terminal, bent in ;a reverse curve and having its free end p'girtion in juxtaposition with said electrode to form a spark gap of predetermined width, the radius of the curve adjacent the shell being greater than the radius adjacent the electrode, said curves being proportioned one to the other to maintain said spark gap the same relative width under various working temperature variations;

3. Aspark plug having a shell, an insulated electrode in said shell, a ground terminal bent in a reverse curve and having one end fixed in said shell and its free'end arranged in a plane substantially parallel with the plane of the end of said electrode to form 'a spark gap of predetermined width, the radius of the curve adjacent the shell being greater than the radius adjacent the electrode, said curves being proportioned one to the other to maintain said spark gap the same relative width under various working temperature variations.

FELIX M. ANTHONY.

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